calvin bradley & arnaud delaval presented at the 2011 meeting of the tire society
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On-Road Fuel Consumption Testing to Determine the Sensitivity Coefficient Relating Changes in Fuel Consumption to Changes in
Tire Rolling Resistance
Calvin Bradley & Arnaud Delaval
Presented at the 2011 meeting of the Tire Society
Page : 2 / 192011 Tire Society Conference
Agenda
Environmental and regulatory context
Rolling resistance basics
Previous results
Derivation of sensitivity coefficient
On-road testing General procedure Methods to monitor fuel consumption Data Analysis
Results
Conclusions
Page : 3 / 192011 Tire Society Conference
Rolling resistance role in production of greenhouse gases
Rolling resistance contribution to over the road transport Passenger vehicles: 20% of forces opposing motion Heavy duty trucks: 30% of forces opposing motion
United States transportation Transportation accounts for 29% of CO2 production The majority comes from over the road vehicles
– Passenger Vehicle: 59%– Heavy Truck: 19%
In the U.S. alone 337 million metric tons (MMT) of CO2 are produced to overcome rolling resistance
1 MMT of CO2 is 200,000 Hot air balloons by volume 1 MMT of CO2 requires almost 800,000 acres of Pine forest to offset
Page : 4 / 192011 Tire Society Conference
Tire Efficiency Labeling Around the World
Final Label TBD
Page : 5 / 192011 Tire Society Conference
Tire Deformations
As a tire is deformed to carry the load three types of deformations are occurring
Bending Compression Shearing
Page : 6 / 192011 Tire Society Conference
Definition of Tire’s Rolling Resistance
Tire’s rolling resistance is characterized by a rolling resistance coefficient :
Tire’s rolling resistance is defined as the energy dissipated by a tire per unit of distance traveled
Ztire
tire
tireRRRR Z
FC ,
7-12 kg/t 4-8 kg/t
001.01 tkg
Driving with 10kg/t tires is as if the vehicle was climbing a permanent 1% slope
Page : 7 / 192011 Tire Society Conference
J. Barrand and J. Bokar established a first order estimate for predicting differences in fuel consumption
The sensitivity coefficient α was further demonstrated to be relatively independent to drive cycle
Empirical prediction Simulations Closed circuit stabilized
speed testing
Previous results
MgCFC RR
Page : 8 / 192011 Tire Society Conference
α
aerodynamic drag
internal frictioninertia
accessories
Example of accessories : air conditioning, power steering, on-board entertainment…
V
P
V
PgM
dt
dVMVACgMCF AccInt
eqDRRRM )sin(2
1 2
gravity
rolling resistance
A vehicle requires energy to move forward and improve the driving comfort
Resistance to Movement characterizes the effort to be overcome
Rolling Resistance is one of the force acting on the vehicle
Rolling Resistance & Resistance to Movement
Page : 9 / 192011 Tire Society Conference
Fuel consumption for at a given moment can be described by;
From previous discussion we know
Engine efficiency is a function of required torque
So efficiency η is also a function of CRR
E
RMFFC
Force Resisting Motion
Energy Density of Fuel
Engine Efficiency
Fuel Consumption (volume per distance)
V
P
V
PgMMVACgMCF Acc
dtdv
dRRRM int221 )sin(
Derivation of Sensitivity Coefficient
0
50
100
150
200
250
300
500 1500 2500 3500 4500 5500 6500engine speed [1/min]
Engin
e t
orq
ue [
Nm
]
Iso engine efficiency
32%
30%31%
13%
21%
29%
27%
Page : 10 / 192011 Tire Society Conference
Derivation of Sensitivity Coefficient
Taking the derivative of fuel consumption with respect to CRR
and simplifying we obtain
Relating this to previous publications then we see
If the change in efficiency with respect to CRR is very small
However, this approximation proves to be insufficient and the second term for α cannot be neglected
MgdCdFC RRE
1
MgCFC RR
MgdCdC
d
Mg
FdFC RR
RRE
RM
E
2
1
RRE
RM
E dC
d
Mg
F
2
1
E
1
Fuel Consumption Testing
Page : 12 / 192011 Tire Society Conference
Test Overview
All tires were machine tested to determine their coefficient of rolling resistance
The impact of these tires on fuel consumption is measured Real world conditions Drive cycle with both urban and city portions Typical E10 gasoline
3 different vehicle segments tested Compact: Toyota Corolla Midsize: Chevrolet Impala Light Truck: Chevrolet Silverado
Wide range of tires evaluated 30 tire sets 10 different brands Approximate range rolling resistance: 7 to 13 kg/t
Page : 13 / 192011 Tire Society Conference
Test Overview
Significant variation can occur during testing
Sources of variation are controlled for consistency as much as possible
Fueling procedures Vehicle factors such as alignment, AC, windows, lights, weight
Other sources of variation are permutated through all tire sets Convoy position Driver Vehicle
Fuel consumption is measured by multiple independent methods
Test length must be sufficient to provide enough data for significant differences between tire sets
Duration of each test ranged from 12,500 km to 23,500 km Results come from approximately 587,000 vehicle kilometers of testing
Page : 14 / 192011 Tire Society Conference
Methods to monitor fuel consumption Fuel pump records
Defines what the consumer actually pays for Measures volume of fuel at ground temperature Data cannot be taken as frequently as other methods Requires a precise fueling procedure
Fuel injector information Measures fuel by injector pulse frequency and duration Vehicle on board fuel economy displays
– Injector data is calibrated by vehicle manufacturer– Can include error from tire diameter variations
Scan Gauge II OBD tool– Injector data must be calibrated for each vehicle – Independent of tire diameter
Inline volumetric flow meters Significant cost Requires cutting of fuel lines for install Measures volume of fuel at fuel line temperatures
Fuel tank
Filter
Runbackfrom engine
Feedlineto engine
Fuel consumption indicator
2000
pu
lses
pe
rlit
er
FeedlineFrom tank
~180 l/h
Fuel tank
Filter
Runbackfrom engine
Feedlineto engine
Fuel consumption indicator
2000
pu
lses
pe
rlit
er
FeedlineFrom tank
~180 l/h
Page : 15 / 192011 Tire Society Conference
Methods Summary Injector Data (Vehicle display & Scan Gauge)
Cost: Low Complexity: Low or Medium Precision: High Accuracy: Low
Fuel Meter (fuel line volumetric meter) Cost: High Complexity: High Precision: High Accuracy: High
Fuel Pump (Service Station Records) Cost: Low Complexity: Medium Precision: Low Accuracy: Highest
Page : 16 / 192011 Tire Society Conference
Results ANOVA analysis was used to correct for driver and vehicle effects
All methods were normalized to fuel pump levels
Results demonstrate agreement between methods
Page : 17 / 192011 Tire Society Conference
Results
ANOVA revealed within a test, fuel consumption changes greater than 1.2% were critically different at 95% confidence
Repeats of testing on each vehicle show similar relationship to CRR
Page : 18 / 192011 Tire Society Conference
Results Testing did not reveal significant differences between
sensitivity coefficients for each vehicle
Thus a single value for α was determined sufficient for all tested vehicles
Value of α confirms that is not small enough to be completely neglected
MgCFC RR
∆FC with lowest RR tire set as reference Measured FC for all testing
km
kgfL
100
*082.0RRdC
d
Page : 19 / 192011 Tire Society Conference
Conclusion
Tire rolling resistance has a significant impact on vehicle fuel consumption
Changes in fuel consumption can bepredicted by the linear empirical model
The sensitivity coefficient α primarily depends on fuel energy density and effective engine efficiency
The sensitivity coefficient α is not strongly a function of vehicle (outside of vehicle weight) or drive cycle
For typical American usage with E10 gasoline fuel savings can be predicted with:
α = 0.082 with ∆FC in L/100km, CRR in kg/t, and Mg in metric tons
α = 1.58E-5 with ∆FC in gal/100miles, CRR in kg/t, and Mg in lbs
MgCFC RR
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